Microphone



June 24, 1924.

E. WEINTRAUB MICROPHONE Filed May 1, 1919 CENTER ATTORNEYS Patented June 24, 1924.

. UNITED STATES EZECHIEL WEINTRAUB OF NEW YORK, N. Y.

MICROPHONE.

Application filed May 1,

To all whom it may concern:

Be it ,known that I, EzEoHIEL IVEINTRAUB, a citizen of the United States, residing at New York, in the county of New York, State of New York, have invented certain new and useful Improvements in Microphones; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as .Will enable others skilled in the art to which it appertains to make and use the same.

The present invention relates to improvements in microphones for the electrical transmission of speech or periodic sounds having a frequency within the range of good audibility, but more particularly to microphones of selective sensitiveness which respond to sounds of a frequency within the range of humanspeech and which respond extremely feebly, or, not at all, to sounds of a very low frequency or aperiodic disturbances such as noises or mechanical shocks.

In the usual type of commercial microphone, carbon granules are loosely confined between two carbon electrodes, of which one is stationary and the other made to vibrate by, the impinging sound waves. Thus, when the microphone is connected in an electric circuit, the contact resistance of the granules varies in unison with the varyingpressure of the vibrating electrode. Physical and electrical properties of the carbon granules permit microphones of this type to respond equally as well to low frequency periodic sounds or aperiodic disturbances as to sounds of the frequency desired to be trans-- mitted.

In the preferred form of my selectively sensitive microphone two carbon electrodes are provided between which are loosely confined carbon coated electrically conductive particles, having a higher specific gravity than carbon, and its action involves, as inv the case of the carbon granule microphone, the variation of contact resistance of the particles in unison with the varying pressure of the vibrating electrode.

The selective sensitiveness of my improved microphone is based on the fact discovered by me, that electrically conductive particles having a higher specific, gravity than carbon, although they respond feebly as compared to the carbon granule type of microphone, respond more feebly to undesirable aperiodic frequencies or low frequency sounds than to sounds Within the range of 1919: Serial N0. 294,062.

frequency of human speech. I have also discovered that the higher thespecific gravity of the particles, the moremarked. is the non-response to undesirable aperiodic dis turbances or low frequency sounds, while the response to frequencies within the range of human speech does not vary in the same proportion with increase in specific gravity.

I have pointed out above that my selec tively sensitive microphone responds more feebly to periodic sounds having a frequency within the range of human speech than carbon "granule microphones, and in order to increase the valueof the current variations produced by the varying resistance of the microphone, it will usually be advantageous to include in apparatus utilizing my improved microphone, means for amplifying the current variations. The most conven lent and efliclent means available for this purpose IS a three-electrode vacuum tube amplifier, by means of which the current variations produced by the microphone may be amplified to any desired value. In this manner, the, response of my selectively sensitive microphone may be made equal to, or

greater than, the response of a carbon granule microphone to any given sound W1th1n the range of frequencyof human speech and at the sametime reduce to a.

ing the arrangement of the particles between the two electrodes;

-Figure 2 is an enlarged cross section of a carboncoated granule or ball as shownoin Figure 2. i y

Fig. 3 illustrates. a method for amplifying the current variations produced by my improved microphone.

Referring now particularly to Fig. 1. which shows a carbon electrode 1, having hemispherical cavities 2 in its surface adapted to retain carbon-coated metallic balls 3, in contact with a carbon electrode 4, adapted to be set into vibration by the impinging sound Waves.

Referring now to Figures 2 and 2 the arrangement of the carbon coated electrically conductive particles 3, is clearly shown with reference to the electrode 1, containing a .cavity 2 retaining the particles 3 so that they are confined between the electrode 1 i and the vibrating electrode 4'. Figure 2 shows a single carbon coated particle 3 which comprises an electrically conductive body 10, preferably of a higher specific gravity than carbon and a carbon coating 11 deposited or placed on the surface thereof.

Referring now to Fig. 3, it will be observed that variations of current in the electric circuit including the electrodes 1 and 4 of my improved microphone, will be amplified by the three-electrode vacuum tube amy human speech. For this reason, an amplifier used in connection with a non-selectively sensitive microphone, such as a carbon granule microphone, produces no material advantage over a carbon granule microphone operating without amplification because the "aperiodic vibrations or other undesi'rable disturbances will be amplified to the same degree as the desired periodic vibrations within the frequency of human speech.

For obvious reasons, the selective sensitiveness of my lmproved microphone recommends its use in connectionwith apparatus located in many environments which would be unfavorable-to the use of carbon granule microphones. For example, in connection with wireless telephone apparatus installed .on an aeroplane where the elimination of motor and propeller noises is important, and in submarine signalling where the elimination of water noises is important. The use of my improved microphone is especially advantageous in connection with apparatus for people hard of hearing and will eliminate the constant buzzing and loud response. to aperiodic-vibrations or other undesirable I disturbances which is an inherent defect in carbon granule microphone apparatus. In long distance telephony, the use of my improved microphone will aid considerably in improving the quality of transmitted tones because of the elimination of noises, etc.

I have. obtained the best results with my improved microphone when metallic 'balls of high specific gravity were used as the varying resistance, particularly balls formed of metalshaving specific gravities betweenthat of copper and that of platinum. How ever, good results have been obtained with metallic balls having a specific gravity less than copper but greater than carbon.

means? In order to obtain the advantages peculiar to contact resistance between carbon surfaces -in microphones and to avoid possible oxidation when using certain metals, and to avoid other chemical action, the balls are preferably coated with a thin layer of car.- bon or graphite. This coating may be accomplished in' any well known manner. For example, by heating the balls in an i on tube to a red heat and passing hydro-carbon vapors through the tube which will decompose and deposit carbon on the balls. If the tube is rotated simultaneously with the deposition of the carbon, an even coating of carbon will be obtained on the surface of the balls. Other methods of coating the balls with carbon such as the slow carbonization of viscous organic material mixed with carbon or graphite applied to the surface of the balls and the simple method of rolling lead balls in fine graphite dust, have yielded good results. I

While I have illustrated my invention as applied to a particular type of microphone, it should be understood that my invention may be utilized inany .type of microphone which depends for its action on a varying resistance loose contact, that modifications may be made in the shape or type of particles'having a specific gravity greater than carbon and :other methods -:-of amplification may be utilized other than that shown in the drawing without departing from the spirit and scope of my invention.

I claim:

1. A selectively sensitive microphone adapted to translate sounds of periodic high frequency into corresponding electric pulsatory. currents, but to respond very feebly to sounds produced by aperiodic or low frequency periodic vibrations comprising, two electrodes adapted to be connected in an electric circuit and carbon coated particles having a higher specific gravity than carbon confined betweensaid electrodes, one of said electrodes adapted to be vibrated by sounds impressed thereon.

2. A selectively sensitive microphone adapted to translate sounds of periodic high frequency into corresponding electric pulsatory currents, but to respond very feebly to sounds produced by aperiodic or low frequency periodic vibrations comprising, two electrodes adapted to be connected in an electric circuit and carbon coated metallic particles having a higher specific gravity' than carbon confined between said electrodes, one of said electrodes adapted to be vibrated by sounds impressed thereon.

3. A- selectively sensitive microphone adapted to translate sounds of periodic high frequency into corresponding electric pulsatory currents, but to respond very feebly to sounds produced by aperiodic or low frequency periodic vibrations comprising, two

' feeble electric pulsatory currents produced satory electric currents,

electrodes adapted to be connected in an electric circuit and carbon coated metallic balls having a higher specific gravity than carbonconfined between said electrodes, one of said electrodes adapted to be vibrated. by sounds impressed'thereon I 4. In electrical apparatus for selectively translating sounds into corresponding pul the combination of a circuit containing a selectively sensitive microphone adapted to translate sounds of periodic high frequency into corresponding feeble electric pulsatory currents, said microphone adapted to respond feebly to sounds produced by aperiodic or low frequency periodic vibrations and comprising two electrodes adapted to be connected in said circuit and having carbon coated particles of a higher specific gravity than'caron confined between said electrodes, and electric current amplifying means associated with said circuit adapted to amplify the in the circuit. I

5. In electrical apparatus for selectively translating sounds into corresponding pulsatory electric currents, the combination of a circuit containing aselectively sensitive microphone adapted to translate sounds of.

periodic high frequency into corresponding feeble electric pulsatory'currents' but to respond very feebly to sounds produced by aperiodic or low frequencyperiodic vibrations and comprising two electrodes adapted to be connected in said circuit having carbon coated metallic balls of a higher specific gravity than carbonconfined between said electrodes, and electric current amplifying means associated with-said circuit adapted to amplify the feeble electric pulsatory currents produced in the circuit.

6. In electrical apparatus for selectively.

translating sounds into satory electric currents, a circuit containing a selectively sensitive microphone adapted to translate sounds of periodic high fr uency into corresponding feeble electric pu satory currents comprising two electrodes adapted to be connected in said circuit having carbon coated metal: lic particles of higher specific gravity than carbon confined therebetween, and a thermionic vacuum tube amplifier associated with said circuit adapted to amplify the feeble electric-pulsatory currents produced in the circuit.

7. The combination, phone, comprising a one-way transmission circuit including sound collecting and reproducing devices, of audio-frequency transforming means, and vacuum tube relay means whose input circuit is connected through said transforming means with said collecting device, and whose output circuit is connected with said reproduclng In testimony whereof I aflix my signature.

EZEOHIEL WEINTRAUB.

corresponding p the combination of in a telephonic audiv device. 

